Brain Spinal cord Central nervous system (CNS) Peripheral nervous system (PNS) Figure 22.1 The human nervous system.

The Nervous System  Meninges protect brain and spinal cord  Dura mater: outermost layer  Arachnoid mater: middle layer  Subarachnoid space contains cerebrospinal fluid (CSF)  Pia mater: innermost layer  Blood–brain barrier

Figure 22.2 The meninges and cerebrospinal fluid. Skull bone Cerebrum Cerebellum Spinal cord Subarachnoid space of spinal cord Subarachnoid space (contains cerebrospinal fluid) Skull bone Dura mater Arachnoid mater Pia mater Blood vessel Cerebrum Cranial meninges Dura mater Arachnoid mater Pia mater Spinal meninges Subarachnoid space (contains cerebrospinal fluid) Central canal

The Nervous System  Meningitis: inflammation of meninges  Encephalitis: inflammation of the brain  Meningoencephalitis: inflammation of both

Bacterial Meningitis  Initial symptoms of fever, headache, and stiff neck  Followed by nausea and vomiting  May progress to convulsions and coma  Diagnosis by Gram stain and latex agglutination of CSF

Figure 22.4 Spinal tap (lumbar puncture). Spinal cord Spinal needle is inserted, usually between the fourth and fifth lumbar vertebrae Fourth lumbar vertebra Cauda equina Sample of cerebrospinal fluid Fifth lumbar vertebra L4 L5 Cerebrospinal fluid Longitudinal section of the spine

Haemophilus influenzae Meningitis  Occurs mostly in children (6 months to 4 years)  Gram-negative aerobic bacteria, normal throat microbiota  Capsule antigen type b  Prevented by Hib vaccine

Neisseria Meningitis  Also called meningococcal meningitis  Caused by N. meningitidis  Gram-negative, aerobic cocci with a capsule  10% of people are healthy nasopharyngeal carriers  Begins as throat infection, rash  Serotypes B, C, Y, W-135  Serotype B & C in United States  Serotype A in Africa  Vaccination (A, C, Y, W-135 capsule) recommended for college students

Figure 22.3 Neisseria meningitis. Cilia N. meningitidis

Streptococcus pneumoniae Meningitis  Also called pneumococcal meningitis  Caused by S. pneumoniae (a gram-positive diplococcus)  70% of people are healthy nasopharyngeal carriers  Most common in children (1 month to 4 years)  Mortality: 30% in children, 80% in elderly  Prevented by vaccination

Listeriosis  Caused by Listeria monocytogenes  Gram-negative aerobic rod  Usually foodborne; it can be transmitted to fetus  Reproduce in phagocytes  Spread phagocyte-to-phagocyte

Figure 22.5 Cell-to-cell spread of Listeria monocytogenes, the cause of listeriosis. Listeria monocytogenes Macrophage Pseudopod Macrophage

Diseases in Focus: Meningitis and Encephalitis. Gram stain of cerebrospinal fluid.

Tetanus  Caused by Clostridium tetani  Gram-positive, endospore-forming, obligate anaerobe  Grows in deep wounds  Tetanospasmin released from dead cells blocks relaxation pathway in muscles  Prevention by vaccination with tetanus toxoid (DTaP) and booster (Td)  Treatment with tetanus immune globulin (TIG)

Advance case of tetanus

Botulism  Caused by Clostridium botulinum  Gram-positive, endospore-forming, obligate anaerobe  Intoxication comes from ingesting botulinal toxin  Botulinal toxin blocks release of neurotransmitter, causing flaccid paralysis  Prevention  Proper canning  Nitrites prevent endospore germination in sausages

Botulism  Treatment: supportive care and antitoxin  Infant botulism results from C. botulinum growing in intestines  Wound botulism results from growth of C. botulinum in wounds

Botulinal Types  Type A toxin  60–70% fatality  Found in CA, WA, CO, OR, NM  Type B toxin  25% fatality  Europe and eastern United States  Type E toxin  Found in marine and lake sediments  Pacific Northwest, Alaska, Great Lakes area

Leprosy  Also called Hansen’s disease  Caused by Mycobacterium leprae  Acid-fast rod that grows best at 30°C  Grows in peripheral nerves and skin cells  Transmission requires prolonged contact with an infected person

Leprosy  Tuberculoid (neural) form: loss of sensation in skin areas; positive lepromin test  Lepromatous (progressive) form: disfiguring nodules over body; negative lepromin test

Figure 22.9 Leprosy lesions. Tuberculoid (neural) leprosyLepromatous (progressive) leprosy

Poliomyelitis (Polio)  Poliovirus  Transmitted by ingestion  Initial symptoms: sore throat and nausea  Viremia may occur; if persistent, virus can enter the CNS  Destruction of motor cells and paralysis occurs in <1% of cases  Prevention: vaccination (enhanced-inactivated polio vaccine)

Figure Worldwide annual incidence of poliomyelitis. Number of confirmed polio cases Year ,000 2,000 3,000 4,000 5,000 6,000 7, ,000 2,000

Rabies  Caused by the rabies virus  Transmitted by animal bite  Furious rabies: animals are restless, then highly excitable  Paralytic rabies: animals seem unaware of surroundings

Figure Pathology of rabies infection. Virus enters tissue from saliva of biting animal. Virus replicates in muscle near bite and enters neuron of peripheral nervous system. Virus moves up peripheral nervous system to CNS. Virus ascends spinal cord. Virus reaches brain and causes fatal encephalitis. Virus enters salivary glands and other organs of victim.

Figure Reported cases of rabies in animals. Skunk Fox Raccoon Fox and skunk KEY Areas of the United States in which rabies predominates in certain wildlife species. Rabies-infected bats were reported in 47 of the 48 contiguous states. In eastern states in which raccoons are the predominant rabies-infected animal, many cases were also reported in foxes and skunks.

Figure Reported cases of rabies in animals. KEY Rabies cases in various wild and domestic animals in the United States. Rabies in domestic animals such as dogs and cats is uncommon because of high vaccination rates. Raccoons, skunks, and bats are the animals most likely to be infected with rabies. Most human cases are caused by bites of bats. Worldwide, most human cases are caused by bites of dogs. Raccoons Bats Skunks Foxes Cats Dogs Cattle Horses/mules Wild Domestic 35.5% 24.8% 24.5% 7.7% 4.6% 1.2% 1.1% 0.6%

Clinical Focus: A Neurological Disease, Figure B. Silver-haired bat.

Rabies Virus  Virus multiplies in skeletal muscles and then brain cells, causing encephalitis  Initial symptoms may include muscle spasms of the mouth and pharynx and hydrophobia

Prevention of Rabies  Preexposure prophylaxis: injection of human diploid cells vaccine (HDCV)  Postexposure treatment: vaccine plus rabies immune globulin (RIG)

Cryptococcus neoformans Meningitis  Also called cryptococcosis  Soil fungus associated with pigeon and chicken droppings  Transmitted by the respiratory route; spreads through blood to the CNS  Mortality up to 30%  Treatment: amphotericin B and flucytosine

Figure Cryptococcus neoformans. Capsule

Chronic Fatigue Syndrome  Also called myalgic encephalomyelitis (ME)  Unexplained fatigue that lasts at least 6 months, plus four of these symptoms:  Sore throat  Tender lymph nodes  Muscle pain  Pain in multiple joints  Headaches  Unrefreshing sleep  Malaise after exercise  Impaired short-term memory or concentration

Chronic Fatigue Syndrome  Experimental treatment promotes antiviral interferons